[do not merge] CI experiments

compiler/rustc_arena/src/lib.rs

@@ -108,7 +108,7 @@ impl<T> ArenaChunk<T> {
 // we stop growing. This scales well, from arenas that are barely used up to
 // arenas that are used for 100s of MiBs. Note also that the chosen sizes match
 // the usual sizes of pages and huge pages on Linux.
-const PAGE: usize = 4096;
+const PAGE: usize = 65536;
 const HUGE_PAGE: usize = 2 * 1024 * 1024;
 
 /// An arena that can hold objects of only one type.

src/bootstrap/src/core/build_steps/compile.rs

@@ -1207,6 +1207,9 @@ pub fn rustc_cargo_env(
             rustc_llvm_env(builder, cargo, target)
         }
     }
+    if builder.config.jemalloc {
+        cargo.env("JEMALLOC_SYS_WITH_LG_PAGE", "16");
+    }
 }
 
 /// Pass down configuration from the LLVM build into the build of